The present invention relates to morphing diagnostic ultrasound images. In particular, diagnostic ultrasound images are transformed for enhancing perfusion assessment. To measure perfusion in an organ, such as the liver or kidney, with ultrasound, added contrast agents or microspheres are injected into a patient. Ultrasound is then used to image the contrast agents as the contrast agents perfuse throughout the organ or tissue of interest. Any of various techniques may be used to detect the contrast agents, such as a loss of correlation between sequential pulses caused by movement or destruction of the contrast agent or B-mode detection. The wash-in or wash-out of contrast agent from the tissue of interest is analyzed to determine a rate or amount of perfusion. The intensity of the detected contrast agent is plotted as a function of time as a curve representing the wash-in or wash-out of the contrast agent.
The time-intensity curve may be inaccurate due to movement. The tissue of interest may move relative to the transducer due to breathing, the effects of the cardiac cycle, unintentional movement of the transducer by the user, or other sources of movement. As a result, the imaged tissue appears to move around within a sequence of ultrasound images. Parameterizing or calculating a time-intensity curve is difficult or inaccurate since a given spatial location in an image may correspond to different locations within the imaged tissue throughout the sequence of images. Due to the breathing or other uncontrollable motion, evaluation of changes that occur at a particular location in an organ or other tissue over time may be erroneous.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiments described below include methods and systems for morphing an ultrasound image for perfusion assessment or other purposes. Various images within a sequence of images or movie clip are mapped to one frame of reference using local warping. Nonlinear local image transformations or other warping based on local estimates of motion are used to interpolate different images to the common reference. The elastic stretching and compression of local image data results in a sequence of images where the same spatial location in each image represents the substantially same spatial location of the imaged tissue. The organ, tissue or region of interest is stationary throughout the sequence of images.
In one aspect, motion is estimated at each of a plurality of local locations between two different ultrasound images representing a same region of tissue or fluid. One ultrasound image is warped as a function of the estimated motions at the different local locations. After warping, a change as a function of time is determined for a same location based on each of the images.
In a second aspect, local estimates of motion of one or more images relative to a reference image are determined, and the images are warped as a function of the estimated motions. Each of the warped images are then displayed as a sequence of images showing the tissue as stationary as a function of time without a decrease in temporal resolution, such as caused by temporal persistence.
Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.